Smokeless powder tester



March 8, 1949.

FIG.

c. HICKMAN ET AL SMOKELESS POWDER TESTER Filed Sept. 2, 1943 25 FIG; 3A.

MENTOR:

CLARENGE /v. H/a/rMAA/a BY ARTHURJOEMPSTE'R ATTORNEY Patented Mar. 8, 1949 UNITED STATES PATENT OFFICE SMOKELESS POWDER TESTER tary of the Navy Application September 2, 1943, Serial No. 501,002

Claims. 1

This invention relates to devices for testing explosives, and more specifically to a device for producing samples of explosives which have been partially burned under specified conditions.

An object of this invention is to provide a device for producing samples of explosives which have been partially burned under conditions similar to those encountered in actual use. By the use of this invention, it is possible, for example, to detect by means of the pitted appearance of the partially burned powder grains, flaws in the powder which result in an uneven rate of burning.

Another object of our invention is to provide a device for testing explosives intended for use in jet propelled devices, by partially burning samples of such explosives under controlled pressure-s so as to approximate closely conditions existing in the intended use of the explosives. Although the device may be used to particular advantage in testing explosives for use in jet propelled devices, we do not intend that its use be limited to such explosives.

A further object of our invention is to provide a device of the character described which will operate without danger of damage to the device. by reason of its inclusion of a pressure limiting shear ring which will give way in case 01" excessive pressures within the device.

A further object of our invention is to provide a device of the character described. which is simple in construction, easy to manufacture, and inexpensive.

These and other objects of the invention may be better understood by reference to the accompanying drawing, in wh ch Fig. 1 is a longitudinal cross sectional view of one form of the new powder testing device;

Figs. 2 and 2A are plan and side views, respectively, of the shear ring employed in the device;

Figs. 3 and 3A are plan and side views, respectively. of the perforated disc employed in the device. and

Fig. 4 is a detail view of the piston partly cut away so as to show how its sections are screwed together.

In the drawing. the numeral designates a cy nder which is threaded internally at each, A threaded base plug l is screwed into the lower end of the cylinder, the base plug having an axial opening extending therethrough. In the upper endof cylinder to is threaded a cylindrical nozzle holder l2 which extends out beyond the end of cylinder 10, a short distance. A recess is formed in the interior of the lower end of nozzle holder it, and in this recess is fitted a shear ring [3 which has an inwardly extending portion 13a serving to retain a nozzle I4 against movement out of the nozzle holder by engaging an outturned lower portion l5 of the nozzle.

Within the cylinder H3 is a piston having a lower portion it, an upper portion l1, and a reduced central portion l8 which is surrounded by a pipe spacer 180., the purpose of which will be explained below. Shoulders Mia and Ila are formed on the piston at the ends of its central portion it. As shown in Fig. 4, the piston is preferably made up of two parts screwed together at IS. The lower portion I6 of the piston is of such diameter that it fits snugly in the axial opening in the base plug H but with sufficient clearance to permit axial movement of the piston relative to the base plug. It is important that the fit between the lower portion ll; of the piston and the base plug be sufficiently tight to retain a combustion-retarding fluid 20, such as water, and prevent the fluid from leaking out of the bottom of the cylinder. The upper portion I! of the piston i considerably smaller in diameter than the lower portion Hi. The annular space 2| between the upper portion of the piston and the opening in nozzle l4 serves a purpose which will be explained below.

A sample-supporting disc 22 is mounted on the piston at the lower end of its upper portion l1 and is retained in place by shoulder Na and by the upper end of pipe spacer [8a. Powder samples are mounted on, the upper surface of the d sc .22 by means of worm head trap rods 24 which are attached. to disc 22 by screw threads or other suitable means. The diameter of disc 22 is smaller than the inner diameter of the casing I0 so that the disc fits loosely in the cylinder. A disc 25. which also fits loosely within the cylinder I0, is mounted on the piston at the upper end of its lower portion [5 and is retained in lace by shoulder I60. and by pipe spacer l8a. This disc may be perforated. if desired. and serves a purpo e which w ll be explained below.

In assembling the device. the base plug H is screwed into place in the lower end of cylinder m, and the cyl nder is then p aced unr eht on a hea y plate having a hole through wh ch the pist n may pass. The base plug l l is stoppered and the fluid All is poured in to a level between discs 22 and after which the piston assembly, toether wi h the powder to be tested. is placed in the chamber of the cylinder, and the nozzle holder !2 with the nozzle contained therein is screwed into the upper end of cylinder Hi. The

electric squib wires (not shown) for igniting he powder sample are passed out through the annular space 2 l.

The operation of the device will now plained. When the powder sample is ignited, the gas pressure in chamber Illa causes the p25 ton and the elements carried by it to move downwardly relative to the casing 99, due to the fact that the cross sectional area of the lower portion E6 of the piston is greater than the cross sec-- tional area of the upper portion ii of the piston. As the disc 25 moves downwardly with the piston, the fluid 20 flows around it and through the per forations in the disc, resulting in a retarding of the movement of the piston. The rate of movement of the piston can be varied by changing the diameter of disc 25 and by changing the number and size of the perforations in the disc. The speed of movement of the piston is also governed by the difference in the cross sectional areas of portions I6 and H, by the inertia of the system, and by frictional forces. Variation of the speed of movement of the piston varies the length of time during which the sample burns, as will be further explained below. The faster the piston moves, the shorter will be the length or" time dur ing which the sample burns, and vice versa.

As the piston moves downwardly, its upper portion moves out of nozzle it until the upper end of the piston clears the base of the nozzle, at which time the gases under compression in chamber Illa suddenly rush out of the nozzle, and the resulting fall of pressure extinguishes the burning powder. By this time, the powder has moved down to the water or other fluid 20 and is prevented from reigniting by being plunged into the fluid. If at any time during the burning of the sample 23, the gas pressure in the device exceeds a predetermined pressure, usually around 10,000 pounds per square inch, the shear ring I3 will give way and nozzle M will be. blown out of the nozzle holder I2. If desired, a sleeve. (not shown) may be provided between the nozzle and the nozzle holder so as. to avoid damage to the nozzle in case the nozzle is. blown out.

An important feature of the invention is the provision of means for closely simulating conditions existing in actual use of the explosive. being tested. The pressure existing in chamber Illa is controlled by the area of the annular space 25 surrounding the upper end ll of the piston. If the area of the annular space, is increased, the pressure will decrease and vice versa. By making the area of the annular space 2| equal to the nozzle area of a given jet propelled device, pressures may be generated in the chamber lilo of the same magnitude as those pr duc d in th j propelled device in which the explosive is to be used as a propellant, and may be maintained at the equilibrium pressure for the desired length of time.

It will be obvious. from. the above description that the conditions under which the sample is tested may be controlled as desired byvarying the clearance between the upper. portion H of the piston and the inner walls of the nozzle, that is, the area of annular space 2 l, to regulate the pressure in the chamber, and by controlling the rate of movement of the piston by means of the dash Dot, including disc 25 and the liquid 20, so as to vary the, time during which the sample is permitted to burn.

We claim:

1". A device for testing explosive compositions,

lit

I at

which comprises a combustion chamber for burning a sample under pressure, means for suddenly releasing said pressure after a predetermined length of time to extinguish the burning sample, a combustion-retarding fluid in said chamber, and means for submerging the residue of the sample in said fluid to secure it against reignition.

2. A device for testing explosive compositions, which comprises a combustion chamber for burning a sample in a limited space under pressure, means for suddenly releasing said pressure after a predetermined length of time to extinguish the burning sample, a combustion-retarding fluid in said chamber, means for submerging the residue of the samplev in said fluid to secure it against reignition, and safety means for releasing said pressure when it exceeds a predetermined limit.

3. A device for producing a partially burned explosive sample, which comprises a cylinder, a combustion-retarding fluid partially filling the cylinder, a plug mounted in the lower end of said cylinder and having an axial passage, a nozzle mounted in the upper end of said cylinder, a piston in said cylinder extending into said nozzle with a substantial clearance and fitting closely in said plug passage, said piston being of larger cross sectional area at the plug end than at the nozzle end, a disc on said piston near the end which extends into the plug and normally confining the fluid between the disc and the plug,

and a sample carrying disc mounted on said piston and disposed in a combustion chamber between said first disc and the nozzle, the piston being operable by combustion pressure in said chamber to withdraw the upper end of the piston from the nozzle and cause said first disc to displace a portion of the fluid into the chamber.

4. A device for producing a partially burned explosive sample, which comprises a cylinder, a

" combustion retarding fluid partially filling the ance and fitting closely in said plug passage, said piston being of larger cross sectional area at the plug end than at the nozzle end, a disc on said piston near the end which extends into the plug and normally confining. the fluid between the disc and the plug, and a sample carrying disc mounted on said piston and disposed in a combustion chamber between said first disc and the nozzle, the piston being operable by combustion pressure in said chamber to withdraw the upper end i of the piston from the nozzle and cause said first disc to displace a portion of the fluid into the chamber.

5. An explosive testing device comprising a cylindrical casing having an annular plug at each end thereof, a combustion-retarding fluid in the casing, a piston having its lower end of greater cross sectional area than its upper end, said piston fitting loosely within the upper plug and fitting sufiiciently tightly Within the lower plug to retain said fluid above said plug while permitting axial movement of said piston relative to said plug, a disc mounted on the piston so as to lie normally in a combustion chamber defined by said upper plug and said fluid, said disk being adapted to support a sample of the explosive to be" tested,

2,464,179 5 a second disc mounted on the plunger below said REFERENCES CITED first disc so as to function as a dashpot when forced into said fluid, and a safety shear ring supporting said upper plug in the casing, whereby The following references are of record in the file of this patent:

said upper plug is blown out by excessive pressure 5 UNITED STATES PATENTS in the casing. Number Name Date CLARENCE N. HICK 1 049,187 Wilson Dec- 3 1912 ARTHUR DEMPSTER- 1,801,449 Olsen et a1 Aug. 30, 1928 

